The absence of malfunction of the color-sensitive pigment in the part of the eye called the retina - the retina is the inner lining of the eye. Color blindness is usually inherited - it's a sex-linked characteristic, carried on the X-chromosome; men are more commonly affected. It's inherited. The most common form I believe is red/green color blindness in which those affected have difficulty distinguishing between red and green. That means that these individuals can benefit from some help putting clothing together - ties, jackets, socks, etc. People with red/green color blindness need to learn other ways of determining whether a stop light is red or green - for example, by knowing the position of the red and green lights on the light fixture.